Primarily though, most completely deaf people think in sign language. Similar to how an “inner voice” of a hearing person is experienced in one's own voice, a completely deaf person sees or, more aptly, feels themselves signing in their head as they “talk” in their heads.

Can deaf people hear their thoughts?

If they've ever heard their voice, deaf people may have a “speaking” internal monologue, but it's also possible that this internal monologue may be present without a “voice.” When asked, most deaf people report that they don't hear a voice at all. Instead, they see the words in their head through sign language.

What language would a deaf person think in?

Hearing-impaired (also referred to as deaf) people think in terms of their “inner voice”. Some of them think in ASL (American Sign Language), while others think in the vocal language they learned, with their brains coming up with how the vocal language sounds.